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/� <br /> GEOMATRIX <br /> Mr. Philip Isorena <br /> California Regional Water Quality Control Board <br /> September 14, 2000 <br /> Page 5 <br /> Geomatrix will evaluate the stability of current groundwater conditions and the <br /> characteristics of the remaining residual non-dissolved petroleum with respect to its ability <br /> to reverse or threaten to reverse this condition. <br /> With respect to the RWQCB's comment about petroleum detections in groundwater, the <br /> final closure request will clarify that dissolved petroleum constituents have not been <br /> detected in groundwater at concentrations above WQOs. <br /> F. Separate phase product has been removed to the extent possible. <br /> Separate phase product (SPP) has been detected in B-4 and GP-7. Chevron considers <br /> these as isolated occurrences of limited extent. I concur that this is true for B-4. <br /> However, the extent of SPP at BGP-7 has not been defined. Chevron should determine its <br /> extent. <br /> During drilling of boring GP-7 in 1995, a sheen was observed on water in the borehole <br /> and therefore no water samples were collected. It isnot uncommon for groundwater in <br /> boreholes advanced through soil affected by crude oil to show a sheen when the soil is <br /> disturbed by activities such as drilling. Monitoring well MW-4 is located within 60 feet <br /> of boring GP-7 and provides a representation of the behavior of undisturbed soil affected <br /> by crude in contact with groundwater in the area and the possible presence of recoverable <br /> separate phase product. No separate phase product or sheen has been observed in MW-4. <br /> Therefore, it does not appear that separate-phase product is present at the site. <br /> G. No existing water supply wells, deeper aquifers, surface waters, or other receptors are <br /> threatened by pollutants remaining in the aquifer. <br /> The report states that no receptors are threatened by migration of dissolved constituents <br /> from shallow groundwater at the site. Chevron asserts that while the groundwater in <br /> direct contact with the residual petroleum in soil is degraded with soluble byproducts, the <br /> latter degrade rapidly as groundwater flows through petroleum polluted oxygen-deficient <br /> saturated soil into the oxygenated subsurface. 1 concur with Chevron that it is unlikely <br /> that the site affects any existing water supply wells. <br /> No response necessary. <br /> H. The total pollutant mass remaining in the groundwater is decreasing at predicted rates <br /> and neither creates, nor threatens to create, a risk to human health and safety or future <br /> beneficial uses of the aquifer. <br /> See comments in Criterion 1. In addition, Chevron needs to estimate when the site would <br /> be cleaned up. <br />